--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/web/lib/django/db/models/query_utils.py Wed Jan 20 00:34:04 2010 +0100
@@ -0,0 +1,244 @@
+"""
+Various data structures used in query construction.
+
+Factored out from django.db.models.query to avoid making the main module very
+large and/or so that they can be used by other modules without getting into
+circular import difficulties.
+"""
+
+import weakref
+from copy import deepcopy
+
+from django.utils import tree
+from django.utils.datastructures import SortedDict
+
+try:
+ sorted
+except NameError:
+ from django.utils.itercompat import sorted # For Python 2.3.
+
+
+class CyclicDependency(Exception):
+ """
+ An error when dealing with a collection of objects that have a cyclic
+ dependency, i.e. when deleting multiple objects.
+ """
+ pass
+
+class CollectedObjects(object):
+ """
+ A container that stores keys and lists of values along with remembering the
+ parent objects for all the keys.
+
+ This is used for the database object deletion routines so that we can
+ calculate the 'leaf' objects which should be deleted first.
+
+ previously_seen is an optional argument. It must be a CollectedObjects
+ instance itself; any previously_seen collected object will be blocked from
+ being added to this instance.
+ """
+
+ def __init__(self, previously_seen=None):
+ self.data = {}
+ self.children = {}
+ if previously_seen:
+ self.blocked = previously_seen.blocked
+ for cls, seen in previously_seen.data.items():
+ self.blocked.setdefault(cls, SortedDict()).update(seen)
+ else:
+ self.blocked = {}
+
+ def add(self, model, pk, obj, parent_model, nullable=False):
+ """
+ Adds an item to the container.
+
+ Arguments:
+ * model - the class of the object being added.
+ * pk - the primary key.
+ * obj - the object itself.
+ * parent_model - the model of the parent object that this object was
+ reached through.
+ * nullable - should be True if this relation is nullable.
+
+ Returns True if the item already existed in the structure and
+ False otherwise.
+ """
+ if pk in self.blocked.get(model, {}):
+ return True
+
+ d = self.data.setdefault(model, SortedDict())
+ retval = pk in d
+ d[pk] = obj
+ # Nullable relationships can be ignored -- they are nulled out before
+ # deleting, and therefore do not affect the order in which objects
+ # have to be deleted.
+ if parent_model is not None and not nullable:
+ self.children.setdefault(parent_model, []).append(model)
+ return retval
+
+ def __contains__(self, key):
+ return self.data.__contains__(key)
+
+ def __getitem__(self, key):
+ return self.data[key]
+
+ def __nonzero__(self):
+ return bool(self.data)
+
+ def iteritems(self):
+ for k in self.ordered_keys():
+ yield k, self[k]
+
+ def items(self):
+ return list(self.iteritems())
+
+ def keys(self):
+ return self.ordered_keys()
+
+ def ordered_keys(self):
+ """
+ Returns the models in the order that they should be dealt with (i.e.
+ models with no dependencies first).
+ """
+ dealt_with = SortedDict()
+ # Start with items that have no children
+ models = self.data.keys()
+ while len(dealt_with) < len(models):
+ found = False
+ for model in models:
+ if model in dealt_with:
+ continue
+ children = self.children.setdefault(model, [])
+ if len([c for c in children if c not in dealt_with]) == 0:
+ dealt_with[model] = None
+ found = True
+ if not found:
+ raise CyclicDependency(
+ "There is a cyclic dependency of items to be processed.")
+
+ return dealt_with.keys()
+
+ def unordered_keys(self):
+ """
+ Fallback for the case where is a cyclic dependency but we don't care.
+ """
+ return self.data.keys()
+
+class QueryWrapper(object):
+ """
+ A type that indicates the contents are an SQL fragment and the associate
+ parameters. Can be used to pass opaque data to a where-clause, for example.
+ """
+ def __init__(self, sql, params):
+ self.data = sql, params
+
+ def as_sql(self, qn=None):
+ return self.data
+
+class Q(tree.Node):
+ """
+ Encapsulates filters as objects that can then be combined logically (using
+ & and |).
+ """
+ # Connection types
+ AND = 'AND'
+ OR = 'OR'
+ default = AND
+
+ def __init__(self, *args, **kwargs):
+ super(Q, self).__init__(children=list(args) + kwargs.items())
+
+ def _combine(self, other, conn):
+ if not isinstance(other, Q):
+ raise TypeError(other)
+ obj = deepcopy(self)
+ obj.add(other, conn)
+ return obj
+
+ def __or__(self, other):
+ return self._combine(other, self.OR)
+
+ def __and__(self, other):
+ return self._combine(other, self.AND)
+
+ def __invert__(self):
+ obj = deepcopy(self)
+ obj.negate()
+ return obj
+
+class DeferredAttribute(object):
+ """
+ A wrapper for a deferred-loading field. When the value is read from this
+ object the first time, the query is executed.
+ """
+ def __init__(self, field_name, model):
+ self.field_name = field_name
+ self.model_ref = weakref.ref(model)
+ self.loaded = False
+
+ def __get__(self, instance, owner):
+ """
+ Retrieves and caches the value from the datastore on the first lookup.
+ Returns the cached value.
+ """
+ assert instance is not None
+ cls = self.model_ref()
+ data = instance.__dict__
+ if data.get(self.field_name, self) is self:
+ data[self.field_name] = cls._base_manager.filter(pk=instance.pk).values_list(self.field_name, flat=True).get()
+ return data[self.field_name]
+
+ def __set__(self, instance, value):
+ """
+ Deferred loading attributes can be set normally (which means there will
+ never be a database lookup involved.
+ """
+ instance.__dict__[self.field_name] = value
+
+def select_related_descend(field, restricted, requested):
+ """
+ Returns True if this field should be used to descend deeper for
+ select_related() purposes. Used by both the query construction code
+ (sql.query.fill_related_selections()) and the model instance creation code
+ (query.get_cached_row()).
+ """
+ if not field.rel:
+ return False
+ if field.rel.parent_link:
+ return False
+ if restricted and field.name not in requested:
+ return False
+ if not restricted and field.null:
+ return False
+ return True
+
+# This function is needed because data descriptors must be defined on a class
+# object, not an instance, to have any effect.
+
+def deferred_class_factory(model, attrs):
+ """
+ Returns a class object that is a copy of "model" with the specified "attrs"
+ being replaced with DeferredAttribute objects. The "pk_value" ties the
+ deferred attributes to a particular instance of the model.
+ """
+ class Meta:
+ pass
+ setattr(Meta, "proxy", True)
+ setattr(Meta, "app_label", model._meta.app_label)
+
+ # The app_cache wants a unique name for each model, otherwise the new class
+ # won't be created (we get an old one back). Therefore, we generate the
+ # name using the passed in attrs. It's OK to reuse an old case if the attrs
+ # are identical.
+ name = "%s_Deferred_%s" % (model.__name__, '_'.join(sorted(list(attrs))))
+
+ overrides = dict([(attr, DeferredAttribute(attr, model))
+ for attr in attrs])
+ overrides["Meta"] = Meta
+ overrides["__module__"] = model.__module__
+ overrides["_deferred"] = True
+ return type(name, (model,), overrides)
+
+# The above function is also used to unpickle model instances with deferred
+# fields.
+deferred_class_factory.__safe_for_unpickling__ = True